ASL (American Sign Language) was my language that I chose for college language requirements, and then as a former Child Developmental Specialist, I did use some sign language with kids with speech problems and a few deaf people.
You need to consider that the deaf are a culture, not a disability. They see themselves as a minority group, not disabled. Deaf people are very private with their language and their social groups, including who they will accept into their circles. This is not my observations, this is what was taught to me in a college course on deaf culture and by an ASL interpreter/teacher. The inner circle is only for people born deaf who grew up signing. Even their own hearing family members are not included in this circle. Then family members of deaf people are much more accepted as teachers and interpreters than people who just happen to have an interest in sign language. People who just like learning sign and want to sing with deaf people are actually viewed with suspicion or at least wariness and it takes a long time to earn their trust and confidence. Deaf people view signing as the best way to communicate. Using hearing aids, cochlear implants, or learning to read lips and speak are all frowned on. If deaf people have deaf children, they pretty much never use anything but sign with their kids.
If you want to be so fluent in sign that you can interpret for people, it is an exhausting job. Interpreting for one hour is a looonnng time in sign. You need breaks or to switch off with another person. If you want to be a teacher that is simultaneously signing to your class, that would be very, very hard and would take years of practice.
I don't know if I answered your question about testing, but I hope I have helped you.